1. Field of the Invention
The present invention relates to improved apparatus and novel methods of operation for cargo container handling cranes having a horizontal gantry supported at an elevated location above the cargo container pickup and deposition areas. More particularly, the present invention relates to the apparatus and reel hod for abating residual sway during cargo container handling by employing a variable level lifting platform, for sway arrest in a cargo container handling crane, which transports containers horizontally along the gantry of the crane, to reduce container transfer cycle times.
2. Description of the Prior Art
The handling and protection of cargo or material during its transportation has been greatly facilitated by the advent of containerization many years ago. Raft mounted dockside gantry cranes having retractable booms have now been long accepted as the standard in the industry for loading and unloading containerized cargo and fungible bulk materials. The containers are moved by the cranes between waterborne vessels and dockside transportation equipment.
When a cargo container transport ship is berthed alongside a dock, a gantry crane is moved along the dock parallel to the ship to a position where a retractable boom can be extended across the beam of the ship above the ship's cells which are the cargo container carrying area. The retractable boom in its operating position extends horizontally outboard from the crane's superstructure and, in its retracted position, clears the superstructure of any ship berthed alongside the dock adjacent to the crane. Containers can be transported along the gantry of the crane between the dockside pickup and deposition area and any storage position located within the beam of a berthed ship in its holds or on its deck.
In the particular form of a gantry crane to which the present invention pertains, the purpose is to move cargo containers a specific horizontal distance from a pickup area to a deposition area. In each operation, in the most usual situation, the pickup area is either a dockside location where a container is picked off of a flatbed trailer or transport truck or railroad car, and moved outboard by the crane and lowered into a shipboard cargo container cell, or the reverse, wherein a container is lifted from a cell onboard ship and moved to a dockside storage area or a truck, trailer, or railroad car.
The gantry portion of the cargo container handling crane of the preferred embodiment of tile present invention includes the retractable boom and a dockside portion and a rear extension of said boom supported by the crane superstructure. However, it is applicable to any crane wherein containers are moved along a gantry from a pickup position to a deposition area. Trolleys run along tile gantry and suspend cargo container lifting spreaders from fleet-through wire rope reeving for attaching to and picking up cargo containers.
In a transfer cycle by a crane, the container must first be picked up, then lifted vertically, moved horizontally, and then lowered to its deposition area. During a portion of the move, vertical and horizontal movement of the container can occur simultaneously. However, for each transfer cycle, the crane must raise or lower a container a specific distance to clear the side of a ship, and a round trip transfer cycle takes a substantial period of time to handle one container.
In addition to the portion of the transfer cycle time required to pickup, lift, move, lower, and deposit the container, there is also a delay at each end of the cycle because of sway or pendulum movement which is induced into the load by virtue of the starting and stopping of the horizontal movement of the container lifting apparatus along the gantry. It takes additional time to abate the sway and to position the container by selectively controlling the forward and reverse movement of the trolley.
Numerous methods and apparatus have been developed for arresting sway in containers and lifting spreaders suspended by wire rope reeving. The problem is most acute at the shoreside container pickup and deposition areas where the containers are picked up or deposited close to ground level from or onto truck or trailer beds, railroad cars, or stacks of containers, and where the lifting spreader is suspended at its longest pendulum length for this purpose. Some of the methods and apparatus for arresting sway in suspended cargo containers are disclosed in the following patents: U.S. Pat. No. 3,375,938 for Anti-Sway Device; U.S. Pat. No. 3,532,324 for Antisway Mechanism; U.S. Pat. No. 3,739,922 for Sway-Arrest System Improvement; U.S. Pat. No. 3,825,128 for Sway-Arrest System; U.S. Pat. No. 3,945,504 for Anti-Sway System for a Spreader Suspended from a Crane; and U.S. Pat. No. 5,186,342 for Integrated Passive Sway Arrest System for Cargo Container Handling Cranes; all of which are assigned to the assignee of the present invention.
A more recent development in the field of cargo container handling is the development of the hatch coverless container ships which unfortunately has Increased the container transfer cycle time in the prior art gantry cranes. These ships were developed to reduce lashing work or container tie down time for containers stacked on the open deck of the ship. This development provides cell guides which project upwards from the deck of the ship and winch therefore require every vertical movement of a container to clear not only the side of the ship but the tops of all the upward projecting cell guides as well winch previously did not extend above the ship's deck.
Therefore, in comparison, when loading and unloading the old type of ship, the container did not always have to be fully lifted a specified height above the deck of the ship. It was only necessary to clear the deck of the ship until containers began to be stacked on top of the deck. At that point, it was still necessary only to lift containers over those already stacked on the deck although when a ship is properly loaded and unloaded, it is accomplished In a way in winch the outboard containers are placed on the ship first and unloaded last so that subsequent containers do not have to be lifted over more than the minimum height of on-deck containers than is necessary.
Further, the container handling productivity for hatch coverless ships is considerably lower in comparison with conventional container ships because the handling pass or transfer cycle on the latter is substantially shorter until stacked containers on the ship gradually increase the time of the handling pass or transfer cycle.
The present invention lowers the cycle transfer time by reducing the time for arresting residual sway of the cargo container lifting apparatus at the shipside deposition and pickup areas. It includes new and novel apparatus and methods of operation. A variable level platform is mounted on the gantry of the crane and telescopes up and down to lift and lower the sheaves which suspend the cargo container lifting spreaders. The platform traverses the gantry between the shoreside and shipside container pickup and deposition areas. It is suspended from trolleys and horizontally transports containers between the areas. This arrangement shortens the length of the wire rope reeving supporting the cargo container lifting spreader when picking up a container or depositing it in the cells of a ship and helps arrest the residual sway in the lifting spreader at the shipside end of the crane.